Organizer with Sent-By is invalid

Currently, the organizer field seems to be wrong when using the sent-by parameter.

According to RFC 5545: The individual calendar address parameter values MUST each be specified in a quoted-string.

Example: ORGANIZER;SENT-BY="mailto:[email protected]":mailto:[email protected]

However, the library generates the value without the quotes: ORGANIZER;SENT-BY=mailto:[email protected]:mailto:[email protected]

The email client interprets the mail as [email protected]:mailto:[email protected] (which means neither the sent-by nor the original email is used, but an invalid combination of both).

I guess this duplicates https://github.com/markuspoerschke/iCal/issues/501